The need to measure small distances (on the order of fractions of a nanometer) and small forces (on the order of pico-newtons) has motivated developments in the field of atomic force microscopy (AFM), which is also referred to as scanning force microscopy (SFM).
AFM devices are important tools in nano-science especially in cellular studies. A conventional AFM device comprises a cantilever with a sharp tip (probe) that is scanned over a cell surface, for example. When the tip contacts the cell surface, forces developed between the tip and the cell cause deflection of the cantilever. AFM devices measure mechanical contact forces, van der Waals forces, capillary forces, chemical bonding forces, electrostatic forces and magnetic forces. Typically, the amount of deflection is measured using a laser spot reflected from a top surface of the cantilever onto an array of photodiodes.
Disadvantageously, a cantilever-based AFM device can measure forces in only one or two dimensions and further requires sophisticated tools to detect these nanometer-scale cantilever deflections. Existing readouts for AFM scanned probe microscopy cantilevers are predominantly based on external (off-chip) displacement sensing systems that typically greatly exceed the size scale of the cantilever sensors themselves.
The sensor design of the present invention was motivated by a need in cell mechanics studies to measure micro-scale and nano-scale forces and cell responses to applied forces in air and liquid environments. Current techniques for measuring micro and nano-scale cell mechanical responses, e.g., AFM devices, are capable of measuring only one- or two-dimensional forces (e.g., normal and frictional forces or normal and torsional forces) and are unnecessarily complex for making simple force measurements. Accurate three dimensional (3-D) response or force sensors are not available.
In view of the disadvantages set forth above, a simple MEMS/NEMS-based force sensor for use in biological or cellular applications that can provide decoupled three dimensional force measurements is needed.